#include<stdio.h>
#include<math.h>

int main(void)
{
	float x1,y1,x2,y2;
	
	while((scanf("%f%f%f%f",&x1,&y1,&x2,&y2))!=EOF)
	{
		printf("%.2f\n",sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)));
	}

	return 0;
}
/*

*/

/*

*/

/*

*/

